A new method is developed for the simultaneous determination of chain orientation and surface concentration in monolayers on liquid substrates. The method is based on the use of s- and p-polarized reflection-absorption (RA) infrared intensities in conjunction with an optical model that includes anisotropy in the optical constants. The advantages and limitations of the method are explored in detail. A modeling assessment of the RA p/RA s ratio leads to information on how the ratio can be used to qualitatively interpret RA spectra. Spectral simulations are given that address the issues of frequency shifting and band distortion in reflection-absorption due solely to optical considerations. Experimental spectra of sodium dodecyl sulfonate are collected as soluble monolayers at the air/water interface. The spectral intensities are used to calculate the chain orientation, the surface concentration, and the associated errors. The surface concentration is compared with that predicted from surface tension isotherms.

The primary emphasis of this work is on the development of an optical model which is descriptive of the reflection-absorption properties from an anisotropic monolayer located on an isotropic liquid substrate. The calculations of electric field intensities, phase changes, and reflection-absorptions are compared for isotropic and anisotropic monolayers in order to explore optical model predictions of chain anisotropy. Relationships are established between the average chain orientation angle, the anisotropic optical constants, and the angle of incident light for s-and p-polarized radiation. The modeling calculations predict that the optimum incident light angles for the extraction of orientation information occur close to the polarizing Brewster angle. A method is proposed whereby the orientation types of isotropy and chain alignment at the isotropic-equivalent angle can be distinguished.